Novel mode-coupling vibrations of AlN thin film bulk acoustic resonator operating with thickness-extensional mode

The dispersion curves of bulk waves propagating in both AlN and ZnO film bulk acoustic resonators(FBARs)are presented to illustrate the mode flip of the thickness-extensional(TE)and 2nd thickness-shear(TSh2)modes.The frequency spectrum quantitative prediction(FSQP)method is used to solve the frequency spectra for predicting the coupling strength among the eigen-modes in AlN and ZnO FBARs.The results elaborate that the flip of the TE and TSh2 branches results in novel self-coupling vibration between the small-wavenumber TE and large-wavenumber TE modes,which has never been observed in the ZnO FBAR.Besides,the mode flip leads to the change in the relative positions of the frequency spectral curves about the TE cut-off frequency.The obtained frequency spectra can be used to predict the mode-coupling behaviors of the vibration modes in the AlN FBAR.The conclusions drawn from the results can help to distinguish the desirable operation modes of the AlN FBAR with very weak coupling strength from all vibration modes.

Bending of a Flexoelectric Semiconductor Plate

We study electromechanical responses of a flexoelectric semiconductor plate in bending under mechanical loads.A two-dimensional theory for classical bending without shear deformation is derived from the three-dimensional macroscopic theory of flexoelectric semiconductors.A simple solution is obtained for pure bending.A combination of physical and geometric parameters is introduced as a measure of the strength of the coupling between the mechanical load and the redistribution of charge carriers.A trigonometric series solution is obtained for a simply supported rectangular plate under a local normal mechanical load,which shows concentration of mobile charges and the formation of electric potential barriers near the loading area.The results are fundamental to the mechanical manipulation of charge carriers in these plates.We also analyze the buckling of a simply supported rectangular plate under in-plane compressive forces.A series of buckling loads and modes are obtained.Numerical results show that flexoelectric coupling exhibits a stiffening effect and increases the buckling load,while semiconduction weakens the flexoelectric stiffening.The distributions of mobile charges in the first few buckling modes are presented.

Magnetically induced electric potential in first-order composite beams incorporating couple stress and its flexoelectric effects

A new model of a first-order composite beam with flexoelectric and piezomagnetic layers is developed.The new model is under a transverse magnetic field and can capture the couple stress and its flexoelectric effects.The governing equations are obtained through a variational approach.To illustrate the new model,the static bending problem is analytically solved based on a Navier’s technique.The numerical results reveal that the extension,deflection,and shear deformation of the current or couple stress relevant flexoelectric model are always smaller than those of classical models at very small scale.It is also found that the electric potentials only appear with the presence of the flexoelectric effect for this non-piezoelectric composite beam model.Furthermore,various electric potential distributions can be manipulated by the particular magnetic fields,and remote/non-contact control at micro-and nano-scales can be realized by current functional composite beams.